Two 60 Percent Design Alternatives for the Redwood Shores Sea Level Rise Protection Project

Alternative 1 preserves multiple future adaptation pathways for the upcoming RSAP planning, and aligns with the objective of reduced reliance on walls discussed at the February council session. Alternative 2 may constrain the City’s ability to adapt over time.

1. Preserving flexibility for future adaptation options is especially important at this stage
   
   This project is moving ahead of the multi-jurisdictional sea level rise planning process required by SB 272 and BCDC’s RSAP. It is therefore critical to avoid design decisions that could constrain future adaptation strategies. Staff has stated that the Redwood Shores project intends to comply with the RSAP, yet the report does not compare the alternatives against RSAP standards or identify which better advances them. The RSAP prioritizes nature-based adaptation, wetland migration, minimizing Bay fill, integrated habitat benefits, adaptive design, and preserving future options. These principles should guide Council’s decision now, in order to avoid a selected levee configuration that forecloses otherwise viable future adaptation strategies.

Alternative 1 in general utilizes a wider footprint, wherever possible, to raise the levee to FEMA+1 height and offers multiple pathways for future adaptation.

Alternative 2 on the other hand proposes adding walls atop much of the existing levee to get to the FEMA+1 height, constraining future adaptation response.

2. The alternatives appear to offer materially different levels of adaptability
   
   One advantage staff repeatedly identified in recommending the FEMA+1 approach, earlier this year, was that its lower initial protection level would substantially reduce the need for floodwalls in Phase One, preserving a more natural levee. This was an important benefit of phasing rather than building immediately to a much higher elevation. As the City selects a 60% design, that benefit should be preserved by avoiding premature reliance on floodwalls, where feasible, and favoring configurations that maintain multiple future adaptation pathways.
   
   We are, therefore, concerned that Alternative 2 is being characterized as an “adaptable design framework.” Its typical cross-sections incorporate walls or constrained structural sections initially, but do not show how they would adapt as sea levels or protection requirements rise. By comparison, Alternative 1 more clearly illustrates an adaptive pathway through a wider levee base that can accommodate future fill and height, or later addition of a low floodwall. Flexibility today is not the same as adaptability over time. Council should understand what future options each configuration preserves, or forecloses.

For sea level rise infrastructure, long-term life-cycle costs, across 50-70 years, should be considered rather than only first-time costs.

If the main downside of Alternative 1 is “first-time” costs, there are several opportunities to reduce the costs as the design is refined.

3. The life-cycle needs and costs of future adaptation should be considered alongside upfront “first-time” costs.
   
   We recognize that Alternative 2 has a lower estimated upfront cost, at approximately $324 million versus $440 million for Alternative 1, and understand this weighs heavily in staff’s recommendation. We suggest, however, that first-time construction costs alone cannot establish which is more adaptable and cost-effective across its adaptive lifetime.
   
   Without understanding how Alternative 2’s wall-based sections could be modified for future conditions, it is difficult to know whether its apparent lower initial cost will remain lower throughout the project’s lifetime. If future protection requires substantial reconstruction or replacement, those savings could be regretted.
   
   Alternative 1’s higher upfront cost estimate reflects its wider levee configuration, a much wider, paved roadtop, Bay Trail requirements, plus many amenities, while potentially allowing future height increases without rebuilding the underlying structure. A meaningful comparison would include some understanding of future maintenance and adaptation needs as sea levels and protection requirements increase.

The 60% design should not foreclose beneficial future adaptation opportunities. Greater reliance on walls may narrow those options and raise additional regulatory challenges later.

4. Nature-based adaptation should be part of the solution.
   
   The staff report states that the project will incorporate nature-based solutions where feasible but does not compare either alternatives’ ability to preserve or expand such opportunities. The RSAP prioritizes nature-based strategies, including buffer space, wetland migration, upland transition zones, and room for future adaptation. In Redwood Shores, opportunities for levee setbacks, ecotone slopes, marsh restoration, and other features have been identified and should be preserved at the 60% design stage.
   
   Alternative 2’s greater reliance on walls could raise issues during BCDC and other agency reviews about nature-based adaptation, habitat impacts, wave action, and long-term adaptability. While its reduced use of fill may offer permitting advantages, its regulatory path is not necessarily simpler. Wall-based designs could limit the City’s ability to address agency concerns, adding both time and changes.